Grounding:
Throughout each day we pick up energy - positive and negative - which can 'overwhelm you' for lack of a better term. Think of a sugar buzz...only alot more intense. Grounding in essence releases the extra energy stored in our bodies and calms us down. Energy doesnt die it cannot be destroyed - it just changes form. Therefore it can be 'recycled' in a sense. When we ground we release our stored up energy into back to the source for it to be recycled into usable energy for another living being - whether that is another human, even you - or a plant or tree.

Shielding:
When we shield we put a protective layer over our body/soul/spirit/mind to protect us from (usually) negative energies that are around us each and every minute of everyday. As with grounding - we are bombarded by both positive, negative, and neutral energy all the time from many different sources. The negative energy can do the most harm and is what we try to shield ourselves from. A shield allows positive energies through and keeps the negative energies out.

I start each day with a ritual of affirming my own good to put the mindset right for the day.  Then I visualize a bubble, similar to one blown from a child's soap bubble pipe, complete with the rainbow patch (rainbows are such mystical/magical symbols of connection, communication, bridges complete with a pot of gold (prosperity) at the end) and see it envelope me totally.  It acts as a filter for all negativity from within or without.